1. Field of the Invention
The present invention relates to a sheet storage cassette and a printing apparatus.
2. Description of the Related Art
Conventionally, printers using roll paper have been widely used as business printers, and some home printers are compatible with roll paper. An advantage of the use of roll paper is that since it is possible to continuously feed paper, when continuous printing is to be performed, it is possible to complete paper feeding operation in a relatively short period of time as compared with feeding of rectangular sheets cut to a predetermined size in advance. For this reason, when continuously printing in large quantities, roll paper is more suitable for high-speed printing. Another advantage of the use of roll paper, other than high-speed printing, is that no marginal portions remain on printed matter.
The reason why marginal portions are required when using rectangular sheets will now be described. A sublimation printer heats sublimation ink to transfer it onto a sheet with the sheet being pressed against an ink ribbon. This leads to large conveyance resistance at the printing unit, resulting in an increase in the load of conveying the sheet at the time of printing. In addition, when printing a color image, the printer reciprocally conveys a sheet to superimpose yellow, magenta, and cyan inks. For this reason, if the amount of sheet feed decreases due to the conveyance load at the time of printing, color misregistration occurs and causes a deterioration in print quality.
In order to maintain print quality, it is necessary to convey paper at the time of printing while reliably gripping the paper with convey rollers from the start of conveyance to the end of conveyance. An unprintable portion always appears in the distance from the thermal head to the convey rollers at the start of printing, and hence the unprintable portion becomes a marginal portion. To handle such a marginal portion, a perforated line is provided to cut off the marginal portion. In addition, as disclosed in Japanese Patent Laid-Open No. 2008-100369, a marginal portion is used as a leg portion to stand paper like a photograph stand. However, a roll paper system free of the trouble of having to cut off marginal portions is more preferable than this method.
Digital cameras have been become popular in recent years. To allow more users to print many photographic data captured by these cameras, it is important to shorten the printing time and save the trouble of cutting off the marginal portions of printed matter. In addition, specifications designed to implement high-speed printing without any marginal portions are required for not only business printers but also home printers.
Another merit of roll paper in terms of the cost per print is that it is easier to achieve low cost in manufacturing roll paper than in manufacturing rectangular sheets with perforated lines. In addition, with regard to the form of supplying consumable materials to users, allowing users to refill only paper wound in roll form can minimize the cost of paper as a consumable material.
As described above, a printer of the roll paper system is required to achieve low-cost and high-speed performance, and the lowest cost usage of roll paper itself is to allow the user place the roll paper which he/she purchased into a roll paper storage cassette, with the shaft being inserted through the roll paper, and load the cassette in the printer main body.
A conventional sublimation printer using rectangular sheets can handle different kinds of sheets, and allows sheets and an ink ribbon to be replaced even when they are not used up. When using the roll paper system, therefore, it is necessary for the printer to be compatible with different paper sizes and allow paper to be replaced even before it is used up.
Consider the roll paper storage cassette disclosed in Japanese Patent Laid-Open No. 2006-306511. With this cassette, when the user removes roll paper before it is used up to replace it, the roll paper unrolls. The user must therefore wind the roll paper again and load it in the roll paper storage cassette.
Roll paper is generally wound with the printing surface being the inner surface, and hence the user does not touch the printing surface. However, when the roll paper unrolls, the user may touch the printing surface. At a portion of the printing surface which the user has touched, sublimated ink becomes difficult to adhere. This may lead to a deterioration in print quality.
For this reason, when using a home printer, it is preferable not to open the roll paper storage cassette until the roll paper is used up once it is loaded in the roll paper storage cassette. In addition, preparing roll paper storage cassettes corresponding to the types of roll paper to be used makes it possible to store the roll paper without contaminating it, prevent errors in detecting the cassette type, and replace it simply by replacing the cassette alone.
In addition, home printers need to be more compact with higher usability. In order to reduce the size of a printer, therefore, it is necessary to reduce the size of roll paper storage cassettes themselves and improve the layout of the paper storage cassette, ink ribbon cassette, cutter unit, and the like so as to reduce the size of the printer main body.
FIGS. 10A and 10B are schematic views each exemplifying a layout for making a printer compact. FIG. 10A shows a standby state. FIG. 10B shows a paper-feeding state. Reference numeral 901 denotes a roll paper storage cassette; 902, an ink ribbon cassette; 903, a feed roller; 904, a grip roller pair; 905, a thermal head; 906, a platen roller; and 907, a cutter.
In the standby state shown in FIG. 10A, the feed roller 903 is at a retreat position, and the roll paper storage cassette 901 is attached to the main body. The roll paper storage cassette 901 is loaded/unloaded in/from the printer main body by being slid in the direction of a roll paper shaft 908 to reduce the opening portion of the printer main body and allow the roll paper storage cassette 901 to be loaded in the main body in the same direction as that in which the ink ribbon cassette 902 is loaded/unloaded. For this purpose, the retreat position of the feed roller 903 must be a position where the roller does not collide with the roll paper storage cassette 901. As shown in FIG. 10A, since a frame 910 of the printer main body or its exterior is located below the feed roller 903 at the retreat position, the rubber diameter of the feed roller 903 is preferably minimized to reduce the size of the printer main body.
At the time of paper feeding shown in FIG. 10B, the feed roller 903 provided in the printer main body moves upward to apply a driving force to the outer surface of roll paper 909 to rotate it in a direction to pick up the leading end of the roll paper from the roll paper storage cassette 901. There are tendencies that as a paper convey path bends, the conveyance load increases, and that as the diameter of the feed roller 903 decreases, the conveying force decreases. For this reason, it is preferable to reduce resistance against the rotation of roll paper. It is especially necessary to make the roll paper shaft 908 smoothly rotate.
With regard to usability, when the user inserts roll paper into the roll paper shaft and loads it into the roll paper storage cassette 901, the roll paper shaft tends to slip off the roll paper. This makes it difficult to insert the roll paper into the roll paper storage cassette 901. This is because the surface of the roll paper shaft described above is made slippery, and there is always a gap between the roll paper shaft and the inner diameter portion of roll paper because the inner diameter tends to vary depending on the roll paper.
There are available methods for positioning a roll paper shaft and roll paper by using a paper tube for the inner diameter of the roll paper and for stopping rotation and supporting a shaft with a complicated mechanism, as disclosed in Japanese Patent Laid-Open No. 2002-326742. In order to implement a simple, low-cost arrangement, however, a method of integrally forming resin springs with a roll paper shaft as a resin component is optimal.
FIG. 11 is a perspective view of an arrangement in which resin springs 908a are integrally provided with the roll paper shaft 908. The resin springs 908a are provided for the roll paper shaft 908 by using a thinning portion formed near the middle portion. A portion of each resin spring 908a which the inner diameter portion of the roll paper 909 contacts has a round shape to prevent it from being caught on the inner diameter portion at the time of loading and at the time of rotation. Although one resin spring is enough to obtain some effect, a pair of resin springs are provided to achieve a balance. When the user inserts the roll paper shaft 908 into the roll paper 909, the pair of resin springs 908a are charged to increase friction to make the roll paper shaft 908 difficult to slip on the roll paper 909.
FIGS. 12A and 12B are sectional views showing the deformation of the resin springs 908a when the roll paper shaft 908 is inserted into the roll paper 909. FIG. 12A shows the resin springs 908a before deformation. FIG. 12B shows the resin springs 908a after deformation. A thinning portion 908b serves as a retreat space for the resin springs 908a. Even when the roll paper shaft 908 is pressed after insertion into the roll paper 909, apexes 908c of the resin springs 908a are located completely inside the outer diameter of the roll paper shaft 908. It is possible to improve usability so as to prevent the resin springs 908a from generating resistance against the conveyance of paper by setting the deformation load of the resin springs 908a to a degree that prevents the roll paper shaft 908 supporting the roll paper 909 from slipping down under its own weight.
However, since the urging force of the resin spring 908a against the inner diameter portion of roll paper is minimized, a reduction in the strength of the resin spring 908a of the roll paper shaft 908 may cause the user to deform the resin spring 908a. If the user greatly deforms the resin spring in its opening direction, the resin spring plastically deforms. As a result, the resin spring is caught on the roll paper at the time of loading. In addition, if the user forcibly inserts the resin spring, deformed in its opening direction, into the inner diameter portion of roll paper, the charged amounts of the resin springs increase to greatly urge the resin springs. This may depress the paper at a position near the inner diameter portion of the roll paper. In addition, the resin springs may be caught on the inner diameter portion of the roll paper when the roll paper rotates during printing. This may make it difficult for the roll paper shaft to smoothly rotate, resulting in affecting the printing operation.
In addition, since the resin springs are provided on the roll paper shaft, the resin springs may collide with a guide member which picks up the leading end of roll paper. The distal end of the pickup guide preferably extends near the roll paper shaft so as to pick up roll paper to the end even if the winding diameter decreases as the printing operation proceeds. As a consequence, the distance between the maximum outer diameter surface of the roll paper shaft and the pickup guide decreases. The resin springs of the roll paper shaft without roll paper being loaded are in an open state. In this state, the resin springs easily make contact with the distal end of the pickup guide. It is assumed that when roll paper is used up or only the roll paper shaft 908 is loaded in the roll paper storage cassette 901, the resin springs spread open. If it is possible to detect the presence/absence of paper, it is possible to prevent the roll paper shaft 908 from rotating. However, since the roll paper storage portion has no detection means, the point at which the presence/absence of paper can be determined is the time when the leading end of paper is detected at the time of paper feeding. The roll paper shaft 908 therefore rotates until this timing.
FIGS. 13A to 13C are sectional views showing the relationship between the resin springs 908a and a pickup guide 911 when loading only the roll paper shaft 908 in the roll paper storage cassette 901, and performing paper feeding operation using the feed roller 903. The pickup guide 911 is a component for picking up the leading end of roll paper on the outermost circumference of the roll paper at the time of paper feeding, and is urged clockwise in FIG. 13A to make contact with the roll paper. FIG. 13A shows a state in which rotation starts, and the resin springs 908a protrude from an outer diameter 908d of the roll paper shaft. At the time of paper feeding, as indicated by the arrow, the feed roller 903 rotates clockwise. When the feed roller 903 rotates to the position in FIG. 13B, the resin spring 908a contacts the bottom surface of the roll paper storage cassette 901. However, since the resin spring 908a deforms, the feed roller 903 can rotate without being caught. When the feed roller 903 rotates to the position in FIG. 13C, however, a pickup guide distal end 911a collides with a side surface of the resin spring 908a, or the pickup guide distal end slides under the resin spring 908a. This may damage the resin spring 908a or the pickup guide 911.